This invention is related to an electrode for use in medical applications, in particular, for an implantable cardiac pacemaker, with an insulated wiring system and at least one electrode for electrical contact with body tissue.
Electrodes of this kind have been generally known for a long time. Examples include unipolar or bipolar electrodes for cardiac stimulation with mono- or multifilar wiring and a great variety of electrodes. A common insulating material is silicon rubber. The silicon rubber meets quite well the requirement of high flexibility, long mechanical life and bodily compatibility that are imposed on the insulation. However, it also tends to expand slightly over the length of the electrode, which can lead to difficulties, particularly in the case of insertion by means of a mandrin, and also when circumstances necessitate removal from the body. In addition, the surface of this insulation is not as smooth as would be desirable for friction-free insertion through the veins and for movement within the veins.
For this reason, a number of experiments have been conducted, to replace silicon rubber with other synthetic materials. Tests with polyurethane have indeed confirmed its good mechanical properties, but there is controversy with regard to its chemical behavior, that is, its reaction to body fluids.
Similarly, polyethylene has not so far been able to offer any improvement. This material appears to be weaker than silicon rubber when exposed to enduring mechanical loads, and is also not quite as flexible.